Carbon fiber manufacturing method

ABSTRACT

A carbon fiber manufacturing method is provided. A carbon fiber precursor fiber bundle is performed with a high-temperature carbonization step to form a carbon fiber, and then the carbon fiber is performed with a plasma surface treatment so that the surface of the carbon fiber is formed with a plasma-modified configuration which is relatively rougher. Finally, the surface of the carbon fiber is coated with a resin oiling agent to obtain the carbon fiber having the resin oiling agent thereon. Particularly, through a plasma surface treatment step, the surface of the carbon fiber is roughened and provided with functional groups, which is beneficial to enhance the interface bonding of the resin oiling agent and the carbon fiber. The structure of the carbon fiber is more stable and reliable. The cost of the carbon fiber production equipment and the working time can be reduced effectively.

FIELD OF THE INVENTION

The present invention relates to a carbon fiber manufacturing technique, and more particularly to a carbon fiber manufacturing method which can greatly improve the sizing quality of a carbon fiber and effectively reduce the cost of the carbon fiber production equipment and the working time.

BACKGROUND OF THE INVENTION

Carbon fibers are classified into carbon fibers or graphite fibers according to their carbon contents, which have excellent mechanical properties and electrical properties and can be widely used in various applications. A conventional carbon fiber is achieved by bundling precursor fibers, such as polyacrylonitrile fibers, to form a carbon fiber precursor fiber bundle, and then the carbon fiber precursor fiber bundle is calcined (high-temperature carbonization) to form the carbon fiber.

There are various precursor fibers of carbon fibers on the market, such as rayon, poly vinyl alcohol, vinylidene chloride, polyacrylonitrile (PAN), pitch, and the like. In general, polyacrylonitrile (PAN) is used as the raw material of carbon fibers. The manufacturing steps are generally as follows: PAN raw material (precursor fiber)→pre-oxidation→high-temperature carbonization→surface treatment→sizing.

In the carbonization step, the carbon fiber precursor fiber bundles are heated to form carbon fibers or graphite fibers by different heating apparatuses according to the application of the carbon fibers. In principle, the carbon content of the fibers of graphite fibers is 90% or more, forming a two-dimensional carbocyclic planar net structure and a graphite layer structure having parallel layers. The results show that the crystalline region of a high-strength carbon fiber is composed of 5-6 graphite layers, and the crystalline region of a high-strength and high-modulus carbon fiber is composed of 10-20 graphite layers. Theoretically and practically, it is pointed out that the larger the crystalline thickness of the graphite layer is, the higher the tensile modulus of the carbon fiber is.

On the other hand, the surface of the carbon fiber after the high-temperature carbonization step is usually coated with a layer of oiling agent (a resin oiling agent is generally used, it is called as a sizing step) before it leaves the factory. The layer of oiling agent is used to protect the fiber from breakage due to friction in the subsequent step to affect the overall quality of the carbon fiber. The surfaces of untreated carbon fibers adsorb impurities thereon. Since these impurities are present between the surface of the carbon fiber and the resin oiling agent, the adhesion between the carbon fiber and the resin oiling agent is insufficient, and the purpose of protecting the fiber cannot be achieved

Furthermore, in the high-temperature carbonization step, the surface of the carbon fiber is excessively finely formed due to high-temperature sintering, and there are few functional groups on the surface. As a result, the fiber and the resin oiling agent cannot be bonded fully in the sizing step. It is known that a heat treatment or electrolysis technique can be applied to the surface treatment of the fiber after the high-temperature carbonization step, and then the sizing step is performed in order to improve the bonding of the fiber and the resin oiling agent.

However, when the surface treatment of the carbon fiber is performed by means of heat treatment, the carbon fiber is treated at a temperature in the range of 500° C. to 800° C. for 1-10 minutes. A relatively long period of time is required. Besides, the heat treatment is always performed with a large number of fibers at a time, so it is difficult to control the processing quality. When the surface treatment of the carbon fiber is performed by means of electrolysis, at least one drying process is required before the surface of the fiber is coated with the oiling agent. This also takes more time. Moreover, a change of the electrolyte may affect the processing quality. Even the surface of the fiber may have depositions.

Accordingly, the inventor of the present invention has devoted himself based on his many years of practical experiences to solve these problems.

SUMMARY OF THE INVENTION

In view of the problems of the prior art, the primary object of the present invention is to provide a carbon fiber manufacturing method which can greatly improve the sizing quality of a carbon fiber and effectively reduce the cost of the carbon fiber production equipment and the working time.

In order to achieve the forgoing object, the carbon fiber manufacturing method of the present invention comprises providing a raw material step, providing a carbon fiber precursor fiber bundle; performing a high-temperature carbonization step, the carbon fiber precursor fiber bundle being heated to form a carbon fiber having a predetermined carbon content; performing a plasma surface treatment step, a plasma gas flow with a predetermined power being provided to act on the carbon fiber at a predetermined time so that a surface of the carbon fiber is formed with a plasma-modified configuration; performing a sizing step, the plasma-modified configuration being coated with a resin oiling agent; and performing a drying step, the resin oiling agent coated on the plasma-modified configuration being processed with drying so that the resin oiling agent is firmly adhered to the surface of the carbon fiber.

In the carbon fiber manufacturing method of the present invention, through the plasma surface treatment step, the surface of the carbon fiber is roughened and provided with functional groups, which is beneficial to enhance the interface bonding of the resin oiling agent and the carbon fiber in the subsequent sizing step so as to improve the sizing quality of the carbon fiber greatly. The structure of the carbon fiber is more stable and reliable. The plasma surface treatment belongs to a dry-type and fast surface treatment technique to effectively reduce the cost of the carbon fiber production equipment and the working time.

Preferably, in the high-temperature carbonization step, the carbon fiber precursor fiber bundle is guided into a chamber. The chamber is formed with at least one microwave field concentration area therein, and is provided with a gas supply module to supply an inert gas and a microwave generating module to supply a high-frequency microwave. Under the protection of the inert gas atmosphere, the electric field of the high-frequency microwave produces a sensing current to heat up and produce a high temperature quickly with the carbon fiber precursor fiber bundle passing through the microwave field concentration area.

Preferably, the chamber is provided with at least one pair of microwave-sensitive materials.

Preferably, the microwave-sensitive materials are one of graphite, carbide, magnetic compound, nitride, and ionic compound or a combination thereof.

Preferably, the inert gas is nitrogen, argon, helium, or a combination thereof.

Preferably, the frequency of the high-frequency microwave is in the range of 300-30,000 MHz, and its microwave power density is in the range of 1-1000 kW/m3.

Preferably, the chamber is an elliptic chamber.

Alternatively, the chamber is a flat panel chamber.

Preferably, in the plasma surface treatment step, the plasma gas flow with a power of 100-10000 watts acts on the carbon fiber for 10-1000 milliseconds.

Alternatively, in the plasma surface treatment step, an atmospheric plasma gas flow with a power of 100-10000 watts acts on the carbon fiber for 10-1000 milliseconds.

Alternatively, in the plasma surface treatment step, a low-pressure plasma gas flow with a power of 100-10000 watts acts on the carbon fiber for 10-1000 milliseconds.

Alternatively, in the plasma surface treatment step, a microwave plasma gas flow with a power of 100-10000 watts acts on the carbon fiber for 10-1000 milliseconds.

Alternatively, in the plasma surface treatment step, a glow plasma gas flow with a power of 100-10000 watts acts on the carbon fiber for 10-1000 milliseconds.

Preferably, the carbon fiber precursor fiber bundle has a surface not processed with a pre-oxidation treatment.

Alternatively, the carbon fiber precursor fiber bundle has a surface processed with a pre-oxidation treatment in advance.

Preferably, the resin oiling agent is a thermosetting resin oiling agent.

Alternatively, the resin oiling agent is a thermoplastic resin oiling agent.

Preferably, the carbon content of the carbon fiber is in the range of 80%-90%.

Specifically, through plasma surface treatment, the surface of the carbon fiber can be roughened and provided with the functional groups, which is beneficial to enhance the interface bonding of the resin oiling agent and the carbon fiber in the subsequent sizing step. The structure of the carbon fiber is more stable and reliable. By the microwave focusing heating way, the same apparatus can be applied to a carbon fiber precursor fiber bundle whose surface has not been processed with a pre-oxidation treatment or a carbon fiber precursor fiber bundle whose surface has been processed with a pre-oxidation treatment in advance. By simply adjusting the microwave power, the apparatus can be used to produce general carbon fibers or high modulus carbon fibers (graphite fibers) so as reduce the cost of the carbon fiber production equipment and the working time effectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of a carbon fiber manufacturing method of the present invention;

FIG. 2 is a structural schematic view of a chamber in accordance with an embodiment of the present invention;

FIG. 3 is a sectional schematic view of a carbon fiber after finishing a plasma surface treatment step in accordance with the carbon fiber manufacturing method of the present invention;

FIG. 4 is a sectional schematic view of a carbon fiber after finishing a sizing step in accordance with the carbon fiber manufacturing method of the present invention;

FIG. 5 is a structural schematic view of a chamber in accordance with another embodiment of the present invention;

FIG. 6a illustrates a SEM image of an object to be tested without plasma treatment; and

FIG. 6b illustrates a SEM image of an object to be tested with the plasma treatment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings.

The present invention discloses a carbon fiber manufacturing method which can greatly improve the sizing quality of carbon fibers and effectively reduce the cost of the carbon fiber production equipment and the working time. As shown in FIG. 1, the carbon fiber manufacturing method of the present invention comprises providing a raw material step, performing a high-temperature carbonization step, performing a plasma surface treatment step, and performing a sizing step. The carbon fiber manufacturing method further comprises performing a drying step after the sizing step. Referring to FIG. 1 through FIG. 5, the steps are described in details as below.

In the step of providing the raw material, a carbon fiber precursor fiber bundle 10A is provided to be processed to form a carbon fiber 10B. In practice, the carbon fiber precursor fiber bundle 10A may be formed of rayon, poly vinyl alcohol, vinylidene chloride, polyacrylonitrile (PAN), pitch, and the like. The surface of the carbon fiber precursor fiber bundle 10A may have not been processed with a pre-oxidation treatment or have been processed with a pre-oxidation treatment in advance.

In the high-temperature carbonization step, the carbon fiber precursor fiber bundle 10A is heated to form the carbon fiber 10B having a predetermined carbon content. In practice, as shown in FIG. 2, the carbon fiber precursor fiber bundle 10A is guided into a chamber 30. The chamber 30 is formed with at least one microwave field concentration area 31 therein, and is provided with a gas supply module 32 to supply an inert gas and a microwave generating module 33 to supply a high-frequency microwave. Under the protection of the inert gas atmosphere, the electric field of the high-frequency microwave produces a sensing current to heat up and produce a high temperature quickly with the carbon fiber precursor fiber bundle 10A passing through the microwave field concentration area 31, enabling the carbon fiber precursor fiber bundle 10A to form the carbon fiber 10B having a predetermined carbon content. The carbon content of the carbon fiber 10B is in the range of 80%-90%.

In the plasma surface treatment step, a plasma gas flow with a predetermined power is provided to act on the carbon fiber 10B at a predetermined time, such that the surface of the carbon fiber 10B is formed with a plasma-modified configuration 11 (shown in FIG. 3) which is rougher or has more functional groups relative to the carbon fiber precursor fiber bundle 10A.

In the sizing step, the plasma-modified configuration 11 on the surface of the carbon fiber 10B is coated with a resin oiling agent 20, so that the surface of the carbon fiber 10B has the resin oiling agent 20, as shown in FIG. 4. In practice, the resin oiling agent 20 is coated on the surface of the carbon fiber 10B by soaking or immersing. The resin oiling agent 20 may be a thermosetting resin oiling agent or a thermoplastic resin oiling agent.

In the drying step, a drying treatment is applied to the resin oiling agent 20 coated on the plasma-modified configuration 11 so that the resin oiling agent 10 is firmly adhered to the surface of the carbon fiber 10B. In practice, the drying treatment is carried out by ultraviolet irradiation, cooling, drying or air-drying for the resin oiling agent to be bonded to the surface of the carbon fiber.

In the plasma surface treatment step, an atmospheric plasma gas flow, a low-pressure plasma gas flow, a microwave plasma gas flow, or a glow plasma gas flow with a power of 100-10000 watts may be used to act on the carbon fiber 10B for 10-1000 milliseconds. Since the plasma gas flow contains particles having energy, the impurities that originally adhere to the surface of the carbon fiber 10B can be broken to form small molecules by the impact of the plasma gas flow through the physical reaction (collision) of the plasma gas flow, and then the small molecules are blown away from the surface of the carbon fiber 10B by the air flow, so that the surface of the carbon fiber 10B is clean. In the sizing step, the resin oiling agent 20 can be completely in contact with the carbon fiber 10B to increase the bonding effect. In addition, the impact of the plasma gas flow will also form the plasma-modified configuration 11 on the surface of the carbon fiber 10B. The plasma-modified configuration 11 is rougher relative to the carbon fiber precursor fiber bundle 10A, and is further formed with pores. The surface of the carbon fiber 10B is roughened or formed with the pores, which is beneficial to increase the contact area between the resin oiling agent 20 and the carbon fiber 10B in the subsequent sizing step. The resin oiling agent 20 penetrates into the pores, and the resin oiling agent 20 is anchored between the pores to form an anchor effect to enhance the bonding effect of the resin oiling agent 20 and the carbon fiber 10B.

The plasma gas flow also makes the surface of the carbon fiber 10B generate a chemical reaction at the same time, so that at least one functional group (such as —OH, —N, etc.) is added to the surface of the carbon fiber 10B. In the sizing step, the surface tension of the surface of the carbon fiber 10B is increased due to the presence of the functional group, which is beneficial to improve the wetting effect for the resin oiling agent to be coated on the carbon fiber 10B. That is, the contact angle of the resin oiling agent 20 to the carbon fiber 10B becomes small, so that the resin oiling agent 20 can be quickly or instantaneously coated on the carbon fiber 10B, and the speed of the sizing step is increased, thereby accelerating the overall production speed of the carbon fiber 10B. The presence of the functional group such as the OH group reacts with the resin oiling agent 20, such as epoxy resin (Epoxy), to generate hydrogen bonding, thereby increasing the bonding effect.

Thereby, in the carbon fiber manufacturing method of the present invention, through the plasma surface treatment step, the surface of the carbon fiber 10B is roughened and provided with functional groups, which is beneficial to enhance the interface bonding of the resin oiling agent 20 and the carbon fiber 10B in the subsequent sizing step so as to improve the sizing quality of the carbon fiber 10B greatly. The structure of the carbon fiber is more stable and reliable. The plasma surface treatment belongs to a dry-type and fast surface treatment technique to effectively reduce the cost of the carbon fiber production equipment and the working time.

Furthermore, the foregoing inert gas may be nitrogen, argon, helium, or a combination thereof. The frequency of the high-frequency microwave may be in the range of 300-30,000 MHz, and its microwave power density may be in the range of 1-1000 kW/m3.

In the embodiment as shown in FIG. 2, the chamber 30 may be an elliptic chamber, or the chamber 30 may be a flat plate chamber as shown in FIG. 5. As shown in FIG. 5, whatever the chamber 30 is, the chamber 30 is provided with a pair of microwave-sensitive materials 34 therein, thereby enhancing the focusing effect on the microwave field in order to further accelerate the high-temperature carbonization process. In practice, the microwave-sensitive materials 34 may be one of graphite, carbide, magnetic compound, nitride, and ionic compound or a combination thereof.

Due to the resonant effect of microwave heating, the carbonization of the carbon fiber is enhanced rapidly and more crystalline carbons are formed and stacked, which leads to the formation of larger graphite crystalline molecules, namely, larger graphite crystalline thickness, while deriving a higher microwave induction heating effect is derived. Such a cycle generates an autocatalytic reaction, enabling the carbon fiber to be rapidly heated to the graphitization temperature (1500-3000° C.), and carbon atoms are reconstructed and rearranged more rapidly to form a graphite layer.

In other words, the same apparatus can be applied to a carbon fiber precursor fiber bundle whose surface has not been processed with a pre-oxidation treatment or a carbon fiber precursor fiber bundle whose surface has been processed with a pre-oxidation treatment in advance. It is only necessary to adjust the microwave power for the production, the apparatus can be used to produce general carbon fibers (1000-1500° C.) or high modulus carbon fibers (graphite fibers).

In a preferred embodiment, an article to be tested that the resin oiling agent 20 after the drying step is firmly adhered to the surface of the carbon fiber 10B, and the treatment conditions in the plasma surface treatment step are shown in Table 1 below:

TABLE 1 the conditions of the plasma surface treatment plasma gas consumption N₂ 200 L/min CDA 0.4 L/min plasma gas amount 200.4 L/min plasma power   0~1000 W plasma surface treatment time 0.025~0.100 sec. carbon fiber yarn width 7 mm yarn per unit time receiving 0.28 J/s capacity distance 1 mm

The ILSS strength (interlayer bonding force) was measured for an object to be tested in an environment of a temperature of 23° C. and a humidity of 50% RH by using an INSTRON measuring machine according to ASTM 2344, and the results are shown in Table 2 below:

TABLE 2 the relationship between the plasma surface treatment power (W), the processing time (sec.) and the interlayer bonding force (MPa) (epoxy resin used as the resin oiling agent) of PAN carbon fiber 12K plasma power (W) of surface interlayer bonding force (ILSS)(MPa) treatment 0.025 sec. 0.075 sec. 0.100 sec. 0(untreated) 70 70 70 250 71 73 75 500 73 76 81 750 75 81 85 900 79 86 88 1000 83 89 91

As can be seen from Table 2, the carbon fiber without the plasma surface treatment, the interlayer bonding force of the object to be tested is only 70 MPa. With an increase of the plasma power, for example, the processing time is 0.075 seconds and the plasma power is increased from the untreated (0 W, without plasma power) to 10000 W, the interlayer bonding force is increased from 70 MPa to 89 MPa. That is, the interlayer bonding force is increased to 127%.

In the sizing step, the epoxy resin is used as the resin oiling agent 20, and the carbon fiber is used as the carbon fiber 10B. FIG. 6a shows a SEM image of the object to be tested without the plasma treatment. FIG. 6b shows a SEM image of the object to be tested with the plasma treatment. As shown in FIG. 6a , the SEM image of the object to be tested without the plasma surface treatment illustrates a void H between the resin oiling agent 20 and the carbon fiber 10B because the surface of the carbon fiber 10B is smooth and doesn't have functional groups. The void H causes a decrease in the strength of the object to be tested. That is to say, the bonding force between the carbon fiber and the resin oiling agent is insufficient for protecting the fiber.

As shown in FIG. 6b , the SEM image of the object to be tested with the plasma surface treatment illustrates that there is no void between the resin oiling agent 20 and the carbon fiber 10B because the surface of the carbon fiber 10B is rough and has functional groups (such as —OH, —N, etc.). The resin oiling agent 20 and the carbon fiber 10B are bonded tightly, so that the strength of the object to be tested is enhanced. That is, the adhesion between the carbon fiber and the resin oiling agent is enhanced, so that the purpose of protecting the fiber can be achieved.

Compared to the prior art, through the carbon fiber manufacturing method of the present invention, the surface of the carbon fiber can be roughened and provided with the functional groups by the plasma surface treatment step, which is beneficial to enhance the interface bonding of the resin oiling agent and the carbon fiber in the subsequent sizing step. The structure of the carbon fiber is more stable and reliable to improve the quality of the carbon fiber, thereby accelerating the overall production speed of the carbon fiber. By the microwave focusing heating way, the same apparatus can be applied to a carbon fiber precursor fiber bundle whose surface has not been processed with a pre-oxidation treatment or a carbon fiber precursor fiber bundle whose surface has been processed with a pre-oxidation treatment in advance. By simply adjusting the microwave power, the apparatus can be used to produce general carbon fibers or high modulus carbon fibers (graphite fibers) so as reduce the cost of the carbon fiber production equipment and the working time effectively.

Although particular embodiments of the present invention have been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the present invention. Accordingly, the present invention is not to be limited except as by the appended claims. 

What is claimed is:
 1. A carbon fiber manufacturing method, comprising: providing a raw material step, providing a carbon fiber precursor fiber bundle; performing a high-temperature carbonization step, the carbon fiber precursor fiber bundle being heated to form a carbon fiber having a predetermined carbon content; performing a plasma surface treatment step, a plasma gas flow with a predetermined power being provided to act on the carbon fiber at a predetermined time so that a surface of the carbon fiber is formed with a plasma-modified configuration; performing a sizing step, the plasma-modified configuration being coated with a resin oiling agent; and performing a drying step, the resin oiling agent coated on the plasma-modified configuration being processed with drying so that the resin oiling agent is firmly adhered to the surface of the carbon fiber.
 2. The carbon fiber manufacturing method as claimed in claim 1, wherein in the high-temperature carbonization step, the carbon fiber precursor fiber bundle is guided into a chamber, the chamber is formed with at least one microwave field concentration area therein, and is provided with a gas supply module to supply an inert gas and a microwave generating module to supply a high-frequency microwave, under the protection of the inert gas atmosphere, an electric field of the high-frequency microwave produces a sensing current to heat up and produce a high temperature quickly with the carbon fiber precursor fiber bundle passing through the microwave field concentration area.
 3. The carbon fiber manufacturing method as claimed in claim 2, wherein the chamber is provided with at least one pair of microwave-sensitive materials.
 4. The carbon fiber manufacturing method as claimed in claim 3, wherein the microwave-sensitive materials are one of graphite, carbide, magnetic compound, nitride, and ionic compound or a combination thereof.
 5. The carbon fiber manufacturing method as claimed in claim 2, wherein the inert gas is nitrogen, argon, helium, or a combination thereof.
 6. The carbon fiber manufacturing method as claimed in claim 2, wherein the frequency of the high-frequency microwave is in the range of 300-30,000 MHz, and its microwave power density is in the range of 1-1000 kW/m3.
 7. The carbon fiber manufacturing method as claimed in claim 2, wherein the chamber is an elliptic chamber.
 8. The carbon fiber manufacturing method as claimed in claim 2, wherein the chamber is a flat panel chamber.
 9. The carbon fiber manufacturing method as claimed in claim 1, wherein in the plasma surface treatment step, the plasma gas flow with a power of 100-10000 watts acts on the carbon fiber for 10-1000 milliseconds.
 10. The carbon fiber manufacturing method as claimed in claim 1, wherein in the plasma surface treatment step, an atmospheric plasma gas flow with a power of 100-10000 watts acts on the carbon fiber for 10-1000 milliseconds.
 11. The carbon fiber manufacturing method as claimed in claim 1, wherein in the plasma surface treatment step, a low-pressure plasma gas flow with a power of 100-10000 watts acts on the carbon fiber for 10-1000 milliseconds.
 12. The carbon fiber manufacturing method as claimed in claim 1, wherein in the plasma surface treatment step, a microwave plasma gas flow with a power of 100-10000 watts acts on the carbon fiber for 10-1000 milliseconds.
 13. The carbon fiber manufacturing method as claimed in claim 1, wherein in the plasma surface treatment step, a glow plasma gas flow with a power of 100-10000 watts acts on the carbon fiber for 10-1000 milliseconds.
 14. The carbon fiber manufacturing method as claimed in claim 1, wherein the carbon fiber precursor fiber bundle has a surface not processed with a pre-oxidation treatment.
 15. The carbon fiber manufacturing method as claimed in claim 1, wherein the carbon fiber precursor fiber bundle has a surface processed with a pre-oxidation treatment in advance.
 16. The carbon fiber manufacturing method as claimed in claim 1, wherein the resin oiling agent is a thermosetting resin oiling agent.
 17. The carbon fiber manufacturing method as claimed in claim 1, wherein the resin oiling agent is a thermoplastic resin oiling agent.
 18. The carbon fiber manufacturing method as claimed in claim 1, wherein the carbon content of the carbon fiber is in the range of 80%-90%. 